Coating composition for ink-jet recording medium and ink-jet recording medium

ABSTRACT

The present invention relates to a coating composition for a recording medium useful in ink jet printing of photographic images to provide a high gloss finish. The coating composition for an ink jet recording medium comprises colloidal silica and a synthetic resin emulsion having two or more glass transition points. The synthetic resin emulsion is obtained by emulsion-polymerizing, simultaneously or separately, (A) a radical-polymerizable unsaturated monomer having a silyl group and (B) another radical-polymerizable unsaturated monomer which is copolymerizable unsaturated monomer which is copolymerizable with (A), in the presence of a radical polymerizable surfactant.

This application is based on JP 201-079186, the priority of which ishereby claimed under 35 U.S.C. § 119. A certified copy of the prioritydocument was submitted on Dec. 29, 2005.

TECHNICAL FIELD OF PERTINENT TO THE INVENTION

The present invention relates to a coating composition for a recordingmedium used in ink jet printing for photographic images having highgloss, more particularly, to a coating composition used in a cast layerformed for imparting gloss on an ink fixation layer. The presentinvention also relates to an ink jet recording medium coated with such acoating composition. An ink jet recording medium coated with thecomposition of the present invention is excellent in its high gloss,weather resistance, a property of following a change of stress caused bybending, and a high ink receiving property.

PRIOR ART

Printing by an ink jet printer is showing a rapid growth recently sincehighly precise images can be enjoyed easily. As the substrate for thisink jet printing, gloss paper and non-gloss paper are usually used, andvarious technological innovations are being made day by day on suchpaper and many patents have been filed with respect to thosetechnologies. Regarding the image formation and fixation mechanism of anink jet recording medium, it is general that anionic ink is printed on asubstrate containing a cationic chemical, pigment and the like, and theanionic component and the cationic component are aggregated to fix theink. In the case of gloss paper, it is mainly observed that a glosslayer applied on an ink fixation layer containing a cationic componenthas minute pores and cracks, and by permeation of ink, the lower inkfixation layer and ink mutually act to cause image formation andfixation.

Japanese Patent Application Laid-Open (JP-A) No. Hei-7-149038/1995suggests that a paint containing a pigment such as colloidal silica andthe like is applied on a polymer having a glass transition point (Tg) of40° C. or more obtained by polymerizing monomers having an ethylenicunsaturated bond, and surface gloss treatment is performed by castcoating at temperatures of the glass transition point or lower under thecondition causing no complete film formation of the polymer, and a layerunder condition of insufficient film formation is formed on the surfaceof paper while maintaining its gloss, thus permeation of ink is promotedand ink is transtered to the lower ink fixation layer. However, in thiscase, the glass transition point is higher than room temperature (40° C.or higher) and poor film formation is intentionally caused; therefore,the gloss layer is very fragile and when ink jet paper is rounded orfolded, many cracks are easily formed on the gloss layer, and otherproblems are observed.

In JP-A No. Hei-10-217601/1998, a water-soluble resin which has arelatively high film-forming-property is used as an adhesive and a largeamount of pigments are mixed to deteriorate film formation to therebyform an ink jet gloss layer; however, such water-soluble resin hasproblems in its poor water resistance, difficulty in freely changing thedegree of Tg which reduces the freedom of designing, like the case ofmonomer having an ethylenic unsaturated bond, and low viscosity which isnot suitable for paint preparation having high concentration, and thelike.

PROBLEMS TO BE SOLVED BY THIS INVENTION

There has been a desire for a coating composition capable of impartingfurther improvement in gloss, improvement in weather resistance and asufficient property to follow the change of stress caused by bending orfolding, which had been insufficient in the prior art, while maintaininga quick ink permeability into an ink receiving layer of cast layercoating agents as in the prior art level.

MEANS FOR SOLVING THE PROBLEMS

It has been found that, according to the present invention, theabove-mentioned problems can be solved by use, in a gloss layer, of acomposition comprising colloidal silica and a synthetic resin emulsionhaving two or more different glass transition points obtained byemulsion-polymerizing simultaneously or seperately (A) aradical-polymerizable unsaturated monomer having a silyl group and (B)another radical-polymerizable unsaturated monomer which iscopolymerizable with (A), in the presence of a radical-polymerizablesurfactant. Namely, by the use of the radical polymerizable surfactantin emulsion polymerization, the scratch resistance of the surface of afilm is improved by the copolymerization of the radical-polymerizableunsaturated monomer having a silyl group (A) without causingbleeding-out of the surfactant on the surface of a film and withoutadversely affecting ink permeability. Further, by the use of thesynthetic resin component having high glass transition point liable toform a discontinuous film, high ink permeability can be manifested; bythe use of the synthetic resin component having low Tg forming a uniformfilm, gloss can be improved, and a property to follow the change instress caused by bending or folding can be improved. In addition, thefragility of a film can be improved. Further, by the presence ofcolloidal silica, ink receiving property can be improved whilemaintaining the transparency of a gloss layer.

In general, a synthetic resin obtained by polymerizing a monomer havinga radical-polymerizable unsaturated bond has a Tg which can be freelydesigned and the temperature can be optionally modified, and byconducting a polymerization reaction under various conditions, asynthetic resin emulsion showing a Tg curve having a plurality ofinflection points can be obtained.

MODES CARRYING OUT THE INVENTION

The present invention relates to a coating composition for ink jetrecording medium comprising colloidal silica and a synthetic resinemulsion having two or more different glass transition points (Tg)obtained by emulsion-polymerizing (A) a radical-polymerizableunsaturated monomer having a silyl group and (B) anotherradical-polymerizable unsaturated monomer which is copolymerzable with(A), in the presence of a radical-polymerizable surfactant, and to anink jet recording medium coated with such a coating composition for inkjet recording medium.

The synthetic resin emulsion constituting the coating composition of thepresent invention is obtained by simultaneously or separatelyemulsion-polymerizing (A) a radical-polymerizable unsaturated monomerhaving a silyl group and (b) which is another radical-polymerizableunsaturated monomer copolymerizable with (A), in the presence of aradical polymerizable surfactant. Particularly, in the presentinvention, for producing a synthetic resin having two or more differentglass transition points, it is necessary to use means for mixing two ormore types of emulsion particles which have been emulsion-polymerizedseparately, and having different glass transition points means for usingmulti-stage polymerization in which the monomer composition duringpolymerization is gradually change, or means for using so-calledpower-feed polymerization in which the monomer composition duringpolymerization is changed at any time.

In the present invention, it is preferable to mix emulsion particlesobtained by separate emulsion-polymerization or to use an emulsionproduced by multi-stage polymerization since the required physicalproperties can be manifested in good balance.

Components constituting the composition of the present invention will bedescribed hereinbelow.

<Monomer Components>

(A) Radical-Polymerizable Unsaturated Monomer Having a Silyl Group

The radical-polymerizable unsaturated monomer having a silyl group (A)of the present invention not only improves the scratch resistance of thesurface of a film owing to the fact the silyl group is hydrolyzed toform a cross-linked structure, but also is expected to exert an effectof coupling an inorganic component such as silicon and the like with thepolymer, and in the present invention where colloidal silica is used, apolymer and colloidal silica are chemically bonded to form a film inwhich both features of an inorganic material and an organic material arecombined together. Specifically, a soft film having high waterresistance and heat resistance is formed.

The radical polymerizable unsaturated monomer having a silyl group (A)used in the present invention is a compound represented by the followinggeneral formula (1) or the general formula (2) having aradical-polymerizable unsaturated bond.R—Si(X)₃  (1)R—Si(R′)(X)₂  (2)

In the above-mentioned general formulae (1) and (2), R represents anorganic group having a vinyl group, (meth) acryloxy group, epoxy group,mercapto group, amino group, isocyanate group and the like. R′represents a lower alkyl group having 1 to 3 carbon atoms. X represent amethoxy group or ethoxy group having a radical-polymerizable unsaturatedbond.

Examples of a monomer having an alkoxysilyl group on the side chaininclude vinylorganoalkoxysilanes such as vinyltrimethoxysilane,vinylmethyldimethoxysilane, vinyldimethylmethoxysilane,vinyltriethoxysilane, vinyl(2-methoxyethoxy)silane,vinyltriacetoxysilane and the like, epoxyorganoalkoxysilanes such asγ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldimethoxysilane,3,4-epoxycyclohexylethyltrimethoxysilane,3,4-epoxycyclohexylethyldimethoxysilane and the like,mercaptoorganoalkoxysilanes such as γ-mercaptopropyltrimethoxysilane andthe like, γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyltriethoxysilane and the like.

In the present invention, these unsaturated monomers (A) may be usedeither alone or in a combination of two or more of them. Of thesemonomers, it is preferable to use, particularly vinyltriethoxysilane and3-methacryloxypropyltriethoxysilane in the present invention, in view ofthe polymerizability.

The amount of the use of the above-mentioned radical polymerizableunsaturated monomer having a silyl group (A) is suitably from 0.1 to 15parts by weight, preferably from 0.5 to 10 parts by weight based ontotal radical polymerizable unsaturated monomers used.

When the amount of the use of the above-mentioned radical polymerizableunsaturated monomer having a silyl group is less than 0.1% by weight,complexation with colloidal silica bicomes insufficient, and waterresistance may decrease, and when the amount is over 15% by weight,instability of polymerization, generation of many aggregates, increasein viscosity, and the like can occur.

(B) Copolymerizable Other Radical-polymerizable Unsaturated Monomer

As another radical-polymerizable unsaturated monomer (B) which iscopolymerizable with (A) used in the present invention, those which canbe used in usual emulsion-polymerization can be used without particularlimitation.

These monomers are composed of a main monomer which is a main componentof a synthetic resin(B-1), and a functional monomer which modifies asynthetic resin to impart further functions (B-2).

Regarding the main monomer (B-1), examples of the monomer which is amain component of the synthetic resin include alkyl (meth)acrylates,cycloalkyl (meth)acrylates, olefins, vinyl esters, aromatic vinylcompounds and the like.

More specifically, as the alkyl (meth)acrylates, cycloalkyl(meth)acrylates, particularly alkyl (meth) acrylates those having in thealkyl group 1 to 12 carbon atoms, such as methyl, ethyl, n-butyl,t-butyl, propyl, 2-ethylhexyl, octyl and the like, and cyclohexylacrylate, cyclohexyl methacrylate and the like.

As the olefin, ethylene and propylene are listed, and in addition, asthe vinyl ester, vinyl acetate, vinyl esters of branched carboxylicacids, vinyl laurate, and the like are listed; and as the aromatic vinylcompound, styrene, α-methylstyrene and the like are listed.

As the functional monomer modifying a synthetic resin (B-2) to impartvarious functions such as storage stability, water resistance, chemicalresistance, weather resistance, adhesion and the like, there are listed,for example, ethylenically unsaturated carboxylic acids which improvestorage stability and adhesion (B-2a), monomers having two or moreradical-polymerizable unsaturated bonds which improve water resistance,weather resistance, chemical resistance, adhesion and the like (B-2b),monomers having an amide group, nitrile group, hydroxyl group, glycidylgroup, methylol group, carbonyl group, quaternary ammonium salt,ethylene oxide chain or chlorine on the side chain, and the like(B-2-others).

As the ethylenically unsaturated carboxylic acid (B-2a), acrylic acid,methacrylic acid, crotonic acid, maleic acid and the like are listed.

As the monomer having two or more radical-polymerizable unsaturatedbonds (B-2b), there are listed divinyl compounds, di(meth)acrylatecompounds, tri(meth)acrylate compounds, tetra(meth)acrylate compounds,diallyl compounds, triallyl compounds, tetraallyl compounds and thelike. More specifically, divinylbenzene, divinyl adipate, ethyleneglycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,polypropylene glycol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,3-butyldi(meth)acrylate, trimethylolethane tri(meth)acrylate,trimethylolpropane tri(meth)acrylate, dipentaerythritoltri(meth)acrylate, diallyl phthalate, triallyl dicyanurate,tetraallyloxyethane and the like.

Regarding other functional monomers (B-2-others), listed as the monomerhaving a hydroxyl group are hydroxyethyl methacrylate, hydroxyethylacrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate,hydroxybutyl methacrylate, hydroxybutyl acrylate and the like; listed asthe monomer having an amide group are acrylamide, methacrylamide and thelike; listed as the monomer having a nitrile group are acrylonitrile andthe like; listed as the monomer having chlorine on the side chain arevinyl chloride, vinylidene chloride and the like, listed as the monomerhaving a glycidyl group are glycidyl methacrylate, glycidyl acrylate;listed as the monomer having a methylol group are N-methylolacrylamideand the like; and listed as the monomer having a carbonyl group areacetacetoxyethyl methacrylate and the like.

In the present invention, as the main monomer (B-1), those preferred arealkyl (meth) acrylates, cycoloalkyl (meth) acrylates, styrene, and vinylesters of branched carboxylic acids. These may be used alone; however,they are used preferably in a combination of two or more of them. Forexample, a combination of two or more alkyl (meth) acrylates andstyrene, a combination of two or more alkyl meth) acrylates, and acombination of vinyl esters of branched carboxylic acids and alkylmethacrylates are preferable from the viewpoint of water resistance,weather resistance, polymerization stability and the like. The use oftwo or more alkyl (meth) acrylates in combination is convenient forcontrol of glass transition point and for improvement of variousproperties.

Further, as the functional monomer (B-2), ethylenically unsaturatedcarboxylic acids are preferable, and this ethylenically unsaturatedcarboxylic acid tends to be oriented over the surface of the syntheticresin emulsion particle, and by partially neutralizing its hydroxylgroup, an electric double layer is formed while contributing to thedispersion stability of the emulsion particles.

As the above-mentioned component (B), at least one of the above-listedcomponents may be used. However, it is preferable to use at least one ormore selected from alkyl (meth)acrylates, cycloalkyl (meth)acrylates,styrene and vinyl esters of branched carboxylic acids in combinationwith at least one or more selected from ethylenically unsaturatedcarboxylic acids as the functional monomer.

<Other Components Used in Polymerization>

The emulsion polymerization according to the present invention may beconducted in an aqueous medium under the addition of other knowncomponents such as surfactants and polymerization initiators. Further,protective colloid, chain transfer agents, pH controlling agents,ultraviolet absorbers, photooxidation inhabitors and the like may beused if desired.

A surfactant functions as an emulsifier in emulsion polymerization, andspecifically, usual anionic, cationic or nonionic surfactants arelisted. In the present invention, radical-polymerizable surfactantshaving one radical-polymerizable unsaturated group in the molecule areparticularly used.

The radical polymerizable surfactant is chemically bonded to the polymercomponent due to the presence of its polymerizable unsaturated bond, andwhen film is formed, it does not bleed out as a liberating surfactant onthe surface of a film. Therefore, bleeding does not occur in ink jetprinting and ink permeates quickly into the fixation layer. When theradical-polymerizable surfactant is not used, liberated surfactantbleeds out on the surface of a film, and ink bleeding occurs uponprinting.

The radical-polymerizable surfactant can be appropriately selected fromknown substances. For example, anionic and nonionic surfactants and thelike are listed, and specific examples thereof include the followingcompounds 1) to 16).

Other surfactants such as anionic and nonionic surfactants having noradical-polymerizable unsaturated bond, and the like can also be used inaddition to the radical-polymerizable surfactant. Namely, as the anionicsurfactant, for example, sodium alkylbenzenesulfonate, sodiumalkylsulfonate, sodium polyoxyethylene alkyl ether sulfonate, and thelike are listed.

As the nonionic surfactant, for example, polyoxyethylene alkylether-type surfactants, polyoxyethylene alkyl ether-type surfactants,polyoxyethylene or polyoxypropylene glycol-type surfactants and the likeare listed.

Regarding these surfactants, all amounts of them may be charged in thepolymerization initiation period, or at least a part of them may beadded dropwise, or they may be used as an emulsified monomer in thepolymerization after being mixed with the monomer. Combination of two ormore of these may be used as well. In the present invention, it ispreferable to mix them with a monomer and to use the mixture as anemulsified monomer in the polymerization from the standpoint ofimproving polymerization stability and control of particle diameter.

The amount of use of all surfactants is from about 0.1 to 20% by weightbased on all monomers. Particularly, it is essential to use aradical-polymerizable surfactant in the present invention, and theamount of use thereof is from 0.3 to 10% by weight, preferably from 0.5to 5.0% by weight based on all monomers used.

When the use amount of use of the radical-polymerizable surfactant isless than 0.3% by weight, the reaction system may be agglomerated, orthe reaction may not be completed. On the other hand, ifnon-radical-polymerizable surfactants are used in an excessive amount toprevent the above-mentioned defects, the surfactant is liberated on thesurface of a coating layer to generate bleeding of ink. When over 10% byweight is used, the viscosity of the reaction system increases toogreatly thus lowering water resistance in some cases.

The polymerization initiator is the one which is radical-decomposed bythe action of heat or a reducing substance to thereby advance theaddition polymerization of monomers, and listed are water-soluble oroil-soluble persulfates, peroxides, azobis compounds and the like, andexamples thereof include potassium persulfate, ammonium persulfate,t-butyl hydroperoxide, hydrogen peroxide, azobisisobutyronitrile (AIBN),rongalite, sodium metabisulfite, and the like. They may be used eitheralone or in combination of two or more. These polymerization initiatorsmay be used together with transition metal ions if desired, and as thetransition metal ion, ferric sulfate, cupric chloride, ferric chlorideand the like are preferable.

As the protective colloid, there can be used without particularlimitation any known substances used in emulsion polymerization, andexamples thereof include polyvinyl alcohol and derivatives thereof,cellulose ether and derivatives thereof, starch derivatives and thelike, and these are used in the form of an aqueous solution.

The chain transfer agent to be used is not restricted to any particulartype and may be appropriately selected from known substances, andexamples thereof include alcohols such as methanol, ethanol, propanol,butanol and the like, carboxylic acids having 2 to 8 carbon atoms suchas acetone, methyl ethyl ketone, cyclohexane, acetophenone,acetaldehyde, propionaldehyde, n-butylaldehyde, furfural, benzaldehydeand the like, mercaptanes such as dodecylmercaptane, laurylmercaptane,n-mercaptane, thioglycolic acid, octyl thioglycolate, thioglycerol andthe like. These may be used either alone or in a combination of two ormore.

As the pH controlling agent, known substances such as ammonia, sodiumhydroxide, potassium hydroxide and the like are listed.

The ultraviolet absorber is not particularly restricted, andbenzophenone derivatives, benzotriazole derivatives are suitably used.These include those having a radical-polymerizable unsaturated bond,that can be preferably copolymerized with the synthetic resincomponents.

As the photooxidation inhibitor, hindered phenol-based substances, andhindered piperidine-based substances are suitably used, and examples ofthe photooxidation inhibitor include, as with the ultraviolet absorber,also those having a radical-polymerizable unsaturated bond, that can bepreferably used since they are copolymerized with the synthetic resincomponents.

According to the present invention, the characteristic feature residesin that a synthetic resin emulsion obtained by emulsion-polymerizationhas at least two or more glass transition points.

Regarding the glass transition point (Tg) of polymers of a syntheticresin emulsion, it is preferable that at least one point be 30° C. orlower, particularly from −50 to 30° C. and at least another point behigher than 30° C., particularly, above 30° C. to 100° C. or lower.Further preferably, at least one point be from −30 to 30° C., and atleast another one point be from 50 to 90° C.

When the lower transition point is 30° C. or lower, a uniform film isobtained after drying and gloss is improved, and additionally, in actualuse, a resin manifests sufficient flexibility, and the cracking of acoating layer on the surface of a recording medium can be suppressed. Onthe other hand, when the higher glass transition point is 30° C. orhigher, microscopic cracks are formed on the coating layer, and ink iscarried quickly into an ink receiving layer through the cracks, so thatink permeability is excellent. Both resin components of the presentinvention can impart the excellent properties simultaneously, andconsequently, the resin components of the present invention can becombined further with other factors to give an extremely excellentcoating composition.

Here, the glass transition point means a temperature at which asynthetic resin particle in a synthetic resin emulsion causes phasetransition from a hard and fragile glass state to a soft rubbery state.The emulsion glass transition point in the present invention means thatthere are at least two phase transition temperatures. In order todetermine the glass transition point, the presence of its inflectionpoint can be easily confirmed by measurement using an analyzer such as adifferential scanning calorimeter (DSC).

For obtaining a synthetic resin emulsion having two or more glasstransition points of the present invention, it is necessary to use anemulsion mixture obtained by separately emulsion-polymerized syntheticresin emulsions, or to use a product from multi-stage polymerization inwhich a monomer composition in the polymerization stage is graduallychanged, or to use a product from a power-feed polymerization method inwhich a monomer composition is changed at any time, further, to use aseed polymerization method, and the like. A film of a synthetic resinemulsion obtained by these polymerization methods shows a differentbehavior from that of a synthetic resin emulsion polymerized from ahomogenenous monomer composition. When using a synthetic resin emulsionobtained by polymerization from a homegeneous monomeric composition, thefilm so obtained exhibits only intermediate physical properties comparedwith those obtained from the respective single monomers as the result ofoffsetting the particular properties of respective single polymers. Thisitself is useful in some applications of the synthetic resin emulsion.However, by specifying a polymerization method as in the presentinvention, a film having contrary physical properties existing togethercan be obtained. The reason for this can be assumed to be that though aformed film is homogenized in macro scale, it includes non-homogeneousparts in micro scale. In the present invention, it is preferable thatseparately polymerized synthetic resin emulsion particles are mixed, ora synthetic resin emulsion obtained by multi-stage polymerization beused.

When synthetic resin emulsions are used in admixture, it is preferable,for example, to mix an acrylate copolymer emulsion or styrene-acrylatecopolymer emulsion having a glass transition point of 30° C. or lowerwith an acrylate copolymer emulsion or styrene-acrylate copolymeremulsion having a glass transition point of 50° C. or higher at themixing ratio of 10:90 to 90:10 (parts by weight) based on non-volatilecomponents reduction.

When the synthetic resin emulsion of the present invention is obtainedby a multi-stage polymerization method, it is preferable, for example,that monomers mainly containing an acrylate of which the composition hasbeen regulated so that the glass transition point is lower than thedesired temperature are firstly emulsion-polymerized; subsequently,monomers mainly containing an acrylate of which composition has beenregulated so that the glass transition point is higher than the desiredtemperature are emulsion-polymerized. Therefore, core-shell shaped,confetti shaped, snow man-shaped emulsion particles can be formed. Inthis case, the ratio of the composition having lower glass transitionpoint to the composition having higher glass transition point ispreferably from 10:90 to 90:10 (parts by weight) in terms ofnon-volatile components reduction.

When the amount of the resin component having lower glass transitionpoint is 10 parts by weight or less, sufficient gloss cannot beobtained, and stress relaxation upon bending becomes insufficient. When90 parts by weight or more, the resulting film is too uniform, andminute pores and cracks for absorbing ink are deficient, and printingaptitude deteriorates.

In the present invention, it is characteristic that colloidal silica isused together with a synthetic resin emulsion.

Colloidal silica is silica sol with ultrafine particles dispersed inwater in the form of colloid, and the diameter of its primary particleis usually in the range from 5 to 100 nm.

In the present invention, any commercially available products can beused, as the above-mentioned colloidal silica, and the colloidal silicamay be surface-treated with a metal ion such as meta-aluminate ion andthe like, or may be mono-dispersed, or particles may be connected in theform of chain or of branch by special treatment.

Among these, those surface-treated with a metal ion such as ameta-aluminate ion and the like are preferable from the viewpoint ofexcellent mixing stability.

Regarding the amount of use of the colloidal silica based on a syntheticresin emulsion, the ratio of synthetic resin emulsion:colloidal silicais preferably from 10:90 to 90:10, preferably from 30:70 to 70:30 basedon non-volatile components.

<Other Components Added to Coating Composition>

In the coating composition of the present invention, various pigments,dyes, coloring pigment thickening agents, pH controlling agents,surfactants, dispersing agents, defoaming agents, anti-freezing agents,releasing agents, ultraviolet absorbers, photoxidation inhibitors andthe like which can be used in an aqueous coating composition can beadded for modifying and improving whiteness, viscosity, flowability,mixing property, preservability, weather resistance, workability and thelike, if necessary.

An ink jet recording medium according to this invention is obtained byapplying the coating composition of the present invention as a glosslayer followed by drying it. In this operation, the material andstructure of the substrate and the ink coated layer are not particularlyrestricted so far as they are generally used in an ink jet recordingmedium. For example, for providing gloss to a medium provided with anink receiving ability to a substrate itself such as paper, film, clothand the like, the gloss layer of the present invention is applied by aknown coating method (comma coater, blade coater, air-knife coated andthe like), the layer is dried and gloss is imparted by these treatments.

For providing ink receiving ability by coating a composition consistingof a pigment, binder, cationic substance having an ink fixing abilityand the like on a substrate, an ink fixation layer is provided. In thecase of paper, cloth and the like, a pigment, binder, cationic substancehaving an ink fixation ability, and the like are impregnated, or addedin a paper making stage, so as to allow at least a part or all of themto be contained inside.

As the pigment, there are listed, for example, inorganic pigments suchas zinc oxide, titanium oxide, calcium carbonate, silic acid, silicate,clay, talc, mica, calcined clay, aluminum hydroxide, barium sulfate,lithopone, silica, colloidal silica and the like; plastic pigments,processed into the form of a sphere, hollow shape, or other variousforms and structures, of polystyrene, polyethylene, polypropylene, epoxyresins, acrylic resins, acryl-styrene copolymers and the like.

As the binder, synthetic and natural polymers can be used. For example,polyvinyl alcohol, denatured polyvinyl alcohol, starch and derivativesthereof, cellulose ether and derivatives, sodium polyacrylate,polyvinylpyrrolidone, acrylamide copolymer, (meth) acrylic acidcopolymer, polyethylene glycol, polyvinyl acetate, polyurethane,urethan-acryl copolymer, ethylene-vinyl acetate copolymer, vinylchloride-vinyl acetate copolymer, styrene-butadiene copolymer,styrene-butadiene-acrylic copolymer, glue, casein, soybean protein,gelatin, sodium arginate and the like.

The coating amount (cast coating amount) of the coating composition ofthe gloss layer in the present invention is preferably from 5 to 50 g/m²(reduced by non-volatile components) and more preferably from 7 to 35g/m² (reduced by non-volatile components).

As the method of drying and gloss imparting after coating, drying by hotair, calendering, casting and the like are used. More specifically, whena coating composition is still wet after coating, it is preferable toset the temperature of a cast roll to 60 to 100° C. upon casting.

Thus obtained ink jet recording medium according to this invention hasextremely remarkable abilities in that it has high gloss, weatherresistance and a degree of follow ability to the change in stress causedby bending or folding, and also has a high ink receiving ability at thesame time.

EXAMPLES Production Example 1

In a polymerization vessel were charged 70 parts by weight of water, 0.4parts by weight of sodium alkylallylsulfosuccinate and 0.2 parts byweight of polyoxyethylene nonylphenyl ether, and they were dissolved bystirring, and heated up to 75° C.; and into this were dropped 10 partsby weight of 4% potassium persulfate and the following emulsifiedmonomer composition over 2 hours while advancing the polymerizationreaction. After completion of dropping, the reaction was kept for agingfor 1 hour to obtain a opalescent synthetic resin emulsion.

Water 50 parts by weight Poyoxyethylene nonylphenyl ether 0.2 parts byweight Sodium alkylallylsulfosuccinate 1.0 parts by weight Methylmethacrylate 30 parts by weight Butyl acrylate 70 parts by weightMethacrylic acid 3 parts by weight Vinyltriethoxysilane 5 parts byweight

To this synthetic resin emulsion was added 2 parts by weight of a 10%ammonia aqueous solution to control pH to about 9. Regarding the glasstransition point of the resulting synthetic resin emulsion particle, theinflection point was observed in the temperature region of 15° C. orlower by measurement by DSC (manufactured by Perkin Elmer).

Production Examples 2 to 8

The same procedure as in Production Example 1 was repeated except thatthe emulsifier in the polymerization vessel and the emulsifier in theemulsified monomer composition, the radical-polymerizable unsaturatedmonomer, the monomer having an alkoxysilyl group on the side chain andthe like were changed. as shown in Table 1.

TABLE 1 Production Example 1 2 3 4 5 6 7 8 Emulsified monomercomposition Methyl methacrylate 30 30 30 30 57 57 30 30 Butylmethacrylate 70 70 — — 43 43 70 — Styrene — — 60 60 — — — 602-ethylhexyl acrylate — — 10 10 — — — 10 Methacrylic acid 3 3 3 3 3 3 33 Vinyltriethoxysilane 5 5 5 5 — — 1 10 3-methacryloxypropyltriethoxy —— — — 5 5 — — silane Sodium 1.0 — — — 0.4 1.0 1.0 1.0alkylallylsulfosuccinate Polyoxyalkylene — 1.0 — — — — — —alkylpropenylphenyl ether sulfate ester salt αsulfo-ω-(1- — — 1.0 1.0 —— — — ((nonylphenoxy)methyl-2-(2- propenyloxy)ethoxy-poly (oxy-1,2-ethanediyl)ammonium salt Polyoxyethylene 0.2 0.2 0.2 — 0.4 0.2 0.2 0.2nonylphenylether Vinyl ether ethoxylate — — — 1.0 — — — — (ethyleneoxide: 50 mol) Emulsifier added to polymerization vessel Sodium 2.0 — —— 0.6 2.0 2.0 2.0 alkyallylsulfosuccinate Polyoxyalkylene — 2.0 — — — —— — alkylpropenylphenyl ether sulfate ester salt αsulfo-ω-(1- — — 2.02.0 — — — — ((nonylphenoxy)methyl-2-(2- propenyloxy)ethoxy-polyethanediyl)ammonium salt Polyoxyethylene 0.2 0.2 0.2 — 0.4 0.2 0.2 0.2nonylphenylether Vinyl ether ethoxylate — — — 1.0 — — — — (ethyleneoxide: 50 mol) Temperature region (° C.) at which 1 point 1 point 1point 1 point 1 point 1 point 1 point 1 point inflection point isobserved when when when when when when when when 15° C. or 15° C. or 70°C. or 70° C. or 30° C. or 30° C. or 15° C. or 70° C. or lower lowerhigher higher lower lower lower higher

Production Example 9

In a polymerization vessel were charged 50 parts by weight of water, 0.4parts by weight of sodium alkylallylsulfosuccinate and 0.2 parts byweight of polyoxyethylene nonylphenyl ether, and they were dissolved bystirring, and heated up to 75° C.; and to this were dropped 13 parts byweight of 4% potassium persulfate and the following emulsified monomercomposition over 3 hours while advancing the polymerization reaction asthe first stage polymerization

Water 30 parts by weight Poyoxyethylene nonylphenyl ether 0.5 parts byweight Sodium alkylallylsulfosuccinate 1.5 parts by weight Methylmethacrylate 30 parts by weight Butyl acrylate 20 parts by weightMethacrylic acid 3 parts by weight 3-Methacryloxypropyltriethoxysilane 2parts by weight

Subsequently, the following emulsified monomer composition and 13 partsby weight of 4% potassium persulfate were added dropwise over 3 hours,and thus polymerization in the second stage was conducted.

Water 30 parts by weight Poyoxyethylene nonylphenyl ether 0.5 parts byweight Sodium alkylallylsulfosuccinate 1.5 parts by weight Styrene 30parts by weight Methyl methacrylate 15 parts by weight 2-Ethylhexylacrylate 5 parts by weight Methacrylic acid 3 parts by weight3-Methacryloxypropyltriethoxysilane 2 parts by weight

After completion of the dropwise addition, aging was conducted for 1hour to obtain a uniform and excellent synthetic resin emulsion. Whenthe glass transition point of the resulted emulsion was measured by DSC,one inflection point was observed in the temperature region of 15° C. orlower, and another inflection point was observed in the temperatureregion of 70° C. or higher, i.e., two inflection points in total.

Production Example 10

In a polymerization vessel were charged 50 parts by weight of water, 0.4parts by weight of sodium alkylallylsulfosuccinate and 0.2 parts byweight of polyoxyethylene nonylphenyl ether, and they were dissolved bystirring, and heated up to 75° C.; and to this were dropped 13 parts byweight of 4% potassium persulfate and the following emulsified monomercomposition over 3 hours while advancing the polymerization reaction asthe first stage polymerization.

Water 30 parts by weight Poyoxyethylene nonylphenyl ether 0.5 parts byweight Sodium alkylallylsulfosuccinate 1.5 parts by weight Styrene 45parts by weight Methyl methacrylate 23 parts by weight 2-ethylhexylacrylate 7 parts by weight Methacrylic acid 3 parts by weight3-methacryloxypropyltriethoxysilane 2 parts by weight

Subsequently, the following emulsified monomer and 13 parts by weight of4% potassium persulfate were added dropwise over 3 hours to carry outthe second stage polymerization.

Water 30 parts by weight Poyoxyethylene nonylphenyl ether 0.5 parts byweight Sodium alkylallylsulfosuccinate 1.5 parts by weight Methylmethacrylate 18 parts by weight Butyl acrylate 12 parts by weightMethacrylic acid 3 parts by weight 3-Methacryloxypropyltriethoxysilane 2parts by weight

After completion of the dropwise addition, aging was conducted for 1hour to obtain a uniform and excellent synthetic resin emulsion. Whenthe glass transition point of the resulted emulsion was measured by DSC,one inflection point was observed in the temperature region of 15° C. orlower, and another inflection point was observed in the temperatureregion of 70° C. or higher, i.e., two inflection points in total.

Comparative Production Examples 1 to 6

The same procedure as in Production Example 1 was repeated except thatthe emulsifier in the polymerization vessel and the emulsifier in theemulsified monomer composition, the radical polymerizable unsaturatedmonomer, the monomer having an alkoxysilyl group on the side chain, andthe like were changed as shown in Table 2.

TABLE 2 Comparative Production Example 1 2 3 4 5 6 Emulsified monomercomposition Methyl methacrylate 30 30 30 30 30 30 Butyl methacrylate 7070 70 — — — Styrene — — — 60 60 60 2-ethylhexyl acrylate — — — 10 10 10Methacrylic acid 3 3 3 3 3 3 Vinyltriethoxysilane — 5 — — 5 — Sodium — —1.0 — — 1.0 alkylallylsulfosuccinate Polyoxyethylene 1.0 1.2 0.2 1.0 1.20.2 nonylphenyl ether Emulsifier added to polymerization vessel Sodium —— 2.0 — — 2.0 alkyallylsulfosuccinate Polyoxyethylene 1.0 2.2 0.2 1.02.2 0.2 nonylphenyl ether Temperature (° C.) at which 1 point 1 point 1point 1 point 1 point 1 point inflection point is observed when 15° C.when 15° C. when 15° C. when 70° C. when 70° C. when 70° C. or lower orlower or lower or higher or higher or higher

Example 1

The synthetic resin emulsion obtained in Production Example 1 in anamount of 30 parts by weight in terms of non-volatile components and thesynthetic resin emulsion obtained in Production Example 3 in an amountof 70 parts by weight in terms of non-volatile components were mixed.When the glass transition point of the resulted synthetic resin emulsionmixture was measured by DSC, one inflection point was observed in thetemperature region of 15° C. or lower, and another inflection point wasobserved in the temperature region of 70° C. or higher, i.e., twoinflection points in total.

To 100 parts by weight of non-volatile components of the above-mentionedsynthetic resin emulsion, colloidal silica in an amount of 120 parts byweight in terms of non-volatile components was combined. Then a coatingcomposition was prepared by further incorporating 5 parts by weight of athickening agent and 2 parts by weight of polyethylene wax as areleasing agent.

An ink fixation layer composed of a pigment, binder and cationicsubstance was applied onto a paper substrate, and the above-preparedcoating solution was coated on its upper layer using a bar coater, andimmediately after that, it was subjected to contact under pressure witha cast drum having a mirror surface having a surface temperature of 80°C. and dried, then, released to obtain an ink jet recording paper havinggloss. At this point, the cast coated amount was 10 g/m² based on termsof non-volatile components.

Examples 2 to 10

The same procedure as in Production Example 1 was repeated except thatthe kind and amount of the synthetic resin emulsions and the amount ofcolloidal silica were changed as shown in Table 3.

Evaluation

Regarding ink jet recording papers having glossiness thus obtained,white paper glossiness, printing ability and folding or bendingresistance were evaluated, and the results are shown in Table 1. Thedetails of the tests are as shown below: White paper glossiness: Thegloss at 75° was measured according to JIS-P8142, and evaluated based onthe following standards:

-   -   ⊚: 65 or more.    -   ◯: 60 or more and less than 65.    -   Δ: 55 or more and less than 60.    -   ×: 55 or less.        Printing ability: Ink jet printing (ISO/JIS-SCID JIS X9201-1995:        N5) was conducted using an ink jet printer PM-770 manufactured        by Seiko Epson Corporation, and its printing ability was        evaluated visually. The standards of evaluation were as follows:    -   ⊚: Excellently printed.    -   ◯: Printed without problems.    -   Δ: Adjacent inks are somewhat intermixed.    -   ×: Inks spread out flow and are mixed, no longer practical.        Folding/bending resistance: The resulted ink jet recording paper        was bent to 90°, and the surface condition at this operation was        visually evaluated.    -   ◯: No cracking observed    -   Δ: Some cracks are observed, but no practical problem.    -   ×: Cracks are formed with crunching sound.        Bend resistant printing ability: After the folding/bending        resistance test, ink jet printing (ISO/JIS-SCID JIS X9201-1995:        N5) was subsequently conducted using the same ink jet printer as        used in the printing ability test and its printing ability was        evaluated visually.    -   ◯: No influence on image after printing.    -   Δ: Some irregularity of image is observed after printing, but no        practical problem.    -   ×: Excellent image is not obtained after printing.

TABLE 3 Example 1 2 2 4 5 6 7 8 9 10 Production 30 30 — — — 70 — — — —Example 1 Production — — 30 — — — — — — — Example 2 Production 70 — — —— 30 — — — — Example 3 Production — 70 70 50 50 — 70 — — — Example 4Production — — — 50 — — — — — — Example 5 Production — — — — 50 — — — —— Example 6 Production — — — — — — 30 50 — — Example 7 Production — — —— — — — 50 — — Example 8 Production — — — — — — — — 100 — Example 9Production — — — — — — — — — 100 Example 10 Temperature 1 point at 1point at 1 point at 1 point at 1 point at 1 point at 1 point at 1 pointat 1 point at 1 point at region (° C.) at 15° C. or 15° C. or 15° C. or15° C. or 15° C. or 15° C. or 15° C. or 15° C. or 15° C. or 15° C. orwhich inflection lower, lower, lower, lower, lower, lower, lower, lower,lower, lower, point is 1 point at 1 point at 1 point at 1 point at 1point at 1 point at 1 point at 1 point at 1 point at 1 point at observed70° C. or 70° C. or 70° C. or 70° C. or 70° C. or 70° C. or 70° C. or70° C. or 70° C. or 70° C. or higher higher higher higher higher higherhigher higher higher higher Colloidal silica 120  120  45 120  120  230 120  120  120 100 White paper ◯ ◯ ⊚ Δ Δ ⊚ ◯ ◯ ◯ ◯ gloss (61) (60) (70)(58) (59) (65) (61) (64) (64) (61) (measured value) Printing ability ⊚ ⊚Δ ◯ ◯ ⊚ Δ ⊚ ⊚ ⊚ Bending Δ Δ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ resistance Bending Δ Δ Δ ◯ ◯◯ ◯ ◯ ◯ ◯ resistant printing ability

Comparative Example 1

The synthetic resin emulsion obtained in Production Example 1 in anamount of 100 parts by weight in terms of non-volatile components, andcolloidal silica in an amount of 120 parts by weight in terms ofnon-volatile components were combined, and a coating compositioncontaining 38% by weight of non-volatile components was prepared afterfurther incorporating 5 parts by weight of a thickening agent and 2parts by weight of polyethylene wax as a releasing agent.

This coating composition was applied in the same manner as in Example 1,to obtain an ink jet recording paper. In this case, the cast coatedamount was 10 g/m² based on terms of non-volatile components.

Comparative Examples 2 to 5

The same procedure as in Comparative Example 1 was repeated except thatthe kind and amount of the synthetic resin emulsions and the amount ofcolloidal silica were changed as shown in Table 4.

TABLE 4 Comparative Example 1 2 3 4 5 Production Example 1 100 — — — —Production Example 3 — 100 — — — Comparative — — 50 — — ProductionExample 1 Comparative — — — 50 — Production Example 2 Comparative — — —— 50 Production Example 3 Comparative — — 50 — — Production Example 4Comparative — — — 50 — Production Example 5 Comparative — — — — 50Production Example 6 Temperature region 1 point at 15° C. 1 point at70°C. 1 point at 15° C. 1 point at 15° C. 1 point at 15° C. (° C.) atwhich or lower or higher or lower and or lower and or lower andinflection point is 1 point at 70° C. 1 point at 70° C. 1 point at 70°C. observed or higher or higher or higher Colloidal silica 120 120 120 120  120  White paper gloss ⊚(80) X(51) O(62) ◯(63) ◯(61) (measuredvalue) Printing ability X ⊚ Δ X Δ Bending resistance ◯ X X Δ X Bendingresistant X X X Δ X printing ability

1. A coating composition for an ink jet recording medium comprising: i)colloidal silica; and ii) a synthetic resin emulsion composition havingtwo or more glass transition (Tg) points, wherein said emulsioncomposition includes a) a first polymeric portion which includes theresidues of a radical-polymerizable unsaturated monomer having a silylgroup, and another radical polymerizable unsaturated monomer; and b) asecond polymeric portion which also includes the residues of a radicalpolymerizable unsaturated monomer having a silyl group, and anotherradical polymerizable unsaturated monomer, wherein the first polymericportion is constituted to provide the emulsion composition with a firstTg point, and the second polymeric portion is constituted to provide theemulsion composition with a second Tg point which is dissimilar from thefirst Tg point, and wherein the first polymeric portion and secondpolymeric portion are separately emulsion polymerized in the presence ofat least one radical polymerizable surfactant, such that the radicalpolymerizable surfactant is present in amounts of from 0.3 to 10% byweight, based on total monomers used in the emulsion composition.
 2. Thecoating composition for an ink jet recording medium according to claim1, wherein at least one of the glass transition points of the syntheticresin emulsion is 30° C. or lower and at least one of the other glasstransition points is over 30° C.
 3. The coating composition for an inkjet recording medium according to claim 1, wherein at least one of thefirst and second polymeric portions comprise, in addition to the silylcontaining monomer, i) at least one monomer selected from alkyl (meth)acrylates, cycloalkyl (meth) acrylates, styrene and vinyl esters ofbranched carboxylic acids, and ii) a functional monomer including atleast one monomer selected from ethylenically unsaturated carboxylicacids.
 4. The coating composition for an ink jet recording mediumaccording to claim 1, wherein the radical polymerizable unsaturatedmonomer(s) having a silyl group in the first and second polymericportions are present in amounts of from 0.1 to 15 parts by weight, basedon total radical polymerizable unsaturated monomers used in the emulsioncomposition.
 5. The coating composition for an ink jet recording mediumaccording to claim 1, wherein a compounding ratio of the synthetic resinemulsion to colloidal silica is from 10:90 to 90:10 based onnon-volatile components.
 6. The coating composition for an ink jetrecording medium according to claim 1, wherein the radical polymerizableunsaturated monomer(s) having a silyl group in the first and secondpolymeric portions are present in amounts of from 0.5 to 10 parts byweight based on total radical polymerizable unsaturated monomers used inthe emulsion composition.
 7. The coating composition for an ink jetrecording medium according to claim 1, wherein the radical polymerizablesurfactant is present in amounts of from 0.5 to 5.0% by weight based ontotal monomers used in the emulsion composition.
 8. The coatingcomposition for an ink jet recording medium of claim 1, wherein at leastone of the glass transition points of the synthetic resin emulsion is15° C. or less, and at least one of the glass transition points is 70°C. or higher.
 9. The coating composition for an ink jet recording mediumof claim 1, wherein at least one of the glass transition points of thesynthetic resin emulsion is in the range of from −30° C. to 30° C. andat least one of the glass transition points is in the range of from 50°C. to 90° C.
 10. The coating composition for an ink jet recording mediumaccording to claim 1, wherein the compounding ratio of the syntheticresin emulsion to colloidal silica is from 30:70 to 70:30 based onnon-volatile components.
 11. The coating composition for an ink jetrecording medium of claim 1, wherein the first polymeric portioncomprises alkyl (meth) acrylate monomers, and the second polymericportion comprises styrene monomers.
 12. The coating composition of claim11, wherein the second polymeric portion comprises a styrene-acrylatecopolymer.
 13. The coating composition according to claim 11, whereinsaid first polymeric portion comprises a butyl (meth)acrylate-methyl(meth)acrylate copolymer.
 14. The coating composition of claim 11,wherein the first polymeric portion provides a glass transition point ofless than 15° C. and the second polymeric portion provides a glasstransition point of greater than 70° C.
 15. The coating compositionaccording to claim 1, wherein the first and second polymeric portionsare nonionic.